1. Field of the Invention
The present invention generally relates to, and more particularly to fixing units and image forming apparatuses, and more particularly to a fixing unit having a battery for supplying power to a heater, an image forming apparatus having such a fixing unit, and a method of determining a temperature detecting position of a temperature sensor.
2. Description of the Related Art
Generally, electrophotography type image forming apparatuses such as copying apparatuses, printers, facsimile apparatuses and composite apparatuses, form a toner image on a recording medium such as recording paper or sheet, and heat the toner image by passing the recording medium through a fixing unit so to fix the toner image on the recording medium.
In the fixing unit, power is supplied to a heater so that the heater heats a fixing member such as a roller and an endless belt. The toner image on the recording medium is heated when the fixing member, such as the roller and the endless belt, contacts the recording medium. Conventionally, the power to the heater is supplied from a commercial A.C. power supply. However, a Japanese Laid-Open Patent Application No. 2002-174988 proposes a fixing unit which is designed so that the power to the heaters of the fixing unit is also supplied using a battery.
In other words, in a case where the fixing unit is started from a stopped state by turning ON a main power supply, for example, it takes time for the fixing unit to reach a usable state, and the fixing unit cannot be used for a waiting time until the usable state is reached. In order to reduce this waiting time, the Japanese Laid-Open Patent Application No. 2002-174988 supplies power to the heaters of the proposed fixing unit by using both the commercial A.C. power supply and the battery, so as to rapidly heat the fixing member to a reload temperature.
But when starting this proposed fixing unit, even if the power supply to the heaters is controlled based on a temperature of the proposed fixing unit that is detected by a temperature sensor, the fixing member may actually be heated to a temperature which exceeds a set temperature. It is undesirable, however, for the temperature of the fixing member to exceed the set temperature.